First Investigation of Seasonal Concentration Behaviors and Sources Assessment of Aliphatic Hydrocarbon in Waters and Sediments from Wadi El Bey, Tunisia.

The contents, composition profiles, and sources of aliphatic hydrocarbons were examined in surface sediment and water samples collected from Wadi El Bey, in Tunisia, during different year seasons in 14 stations receiving domestic effluent, industrial discharge, and agricultural drainage wastes. The target substances were analyzed by gas chromatography coupled with mass spectrometric detection (GC/MS). Total concentrations of n-alkanes (n-C14-n-C38) ranged from 0.08 ± 0.01 to 18.14 ± 0.1 µg/L in waters and 0.22 ± 0.04 to 31.9 ± 24.6 µg/g in sediments, while total aliphatic fraction ranged from 0.08 ± 0.01 to 196 ± 140 µg/L in waters and 0.22 ± 0.04 to 1977 ± 1219 µg/g in sediments, which means that almost all sites were affected by hydrocarbon contents in sediments exceeding the recommended limit (100 µg/g). Various diagnostic indices (ADIs) were used to identify the hydrocarbon sources, namely the concentration ratios of individual compounds (n-C17/pristane, n-C18/phytane, pristane/phytane, n-C29/n-C17, n-C31/n-C19) as well as cumulative quantities (Carbon Preference Index, natural n-alkanes ratio, terrigenous/aquatic compounds ratio, unresolved complex mixture percentage, low molecular weight vs. high molecular weight homologues, Alkane Proxy and Terrestrial Marine Discriminants). In general, these indexes indicated that the origin of aliphatic hydrocarbons affecting sediments and waters of Wadi El Bey were linked to both biogenic and petrogenic inputs, attesting the impact of plankton and terrestrial plants and of oil contamination, respectively. The average carbon chain length computation (ACL), used to further index the chemical environment, ranged from 25.5 to 31.1 in sediments and 47.9-116 in waters. This finding could depend on the severe disturbances suffered by the ecosystem as a consequence of heavy anthropogenic inputs. Petroleum contamination associated with high eutrophication rates in Wadi El Bey must be strictly controlled, due to possible harmful effects induced on ecosystem and humans.

Seasonal occurrence, source evaluation and ecological risk assessment of polycyclic aromatic hydrocarbons in industrial and agricultural effluents discharged in Wadi El Bey (Tunisia).

Polycyclic aromatic hydrocarbons are of great concern due to their persistence, bioaccumulation and toxic properties. The occurrence, source and ecological risk assessment of 26 polycyclic aromatic hydrocarbons in industrial and agricultural effluents affecting the Wadi El Bey watershed were investigated by means of gas chromatographic/mass spectrometric analysis (GC/MS). Total PAHs (∑ 26 PAH) ranged from 1.21 to 91.7 µg/L. The 4- and 5-ring compounds were the principal PAHs detected in most of 5 sites examined. Diagnostic concentration ratios and molecular indices were performed to identify the PAH sources. Results show that PAHs could originate from petrogenic, pyrolytic and mixed sources. According to the ecotoxicological assessment, the potential risk associated with PAHs affecting agricultural and industrial effluents ranged from moderate to high for both aquatic ecosystem and human health. The toxic equivalency factor (TEF) approach indicated that benzo[a]pyrene and benz[a]anthracene were the principal responsible for carcinogenic power of samples.

Seasonal Distribution, Source Identification, and Toxicological Risk Assessment of Polycyclic Aromatic Hydrocarbons (PAHs) in Sediments from Wadi El Bey Watershed in Tunisia.

Surface sediments were collected from the Watershed of Wadi El Bey in Tunisia to evaluate the degree of polycyclic aromatic hydrocarbons (PAHs) contamination. Sediments were collected during different seasons in 14 sites that received wastes from domestic effluent, industrial discharge, and agricultural drainage wastes. Twenty-six individual PAHs were analyzed. The total PAH contents (Σ PAHs) in surface sediments showed wide variability, ranging from 6.89 ± 0.05 to 340 ± 0.1 ng g-1. The 4-, 5-, and 6-ring compounds were the most abundant PAHs detected at the majority of sites. Diagnostic concentration ratios between pairs of PAHs and molecular indices, calculated with the purpose of drawing information about pollution sources, indicated that PAHs were of both petrogenic and pyrolytic origins. Toxic contaminants concentrations were determined according to the numerical effect-based sediment quality guidelines (SQGs). PAH levels did not exceed the SQGs, indicating that PAHs seem to pose low and occasional toxicity risks. Total carcinogenicity and mutagenicity (TEQBaP and MEQBaP) ranged from 0.08 to 65 ng and from 0.02 to 135.0 ng g-1 of dry weight, respectively. Among the seven carcinogenic PAHs, BaP accounted for the majority of the potency and could potentially be used as a unique indicator of PAH toxicity. This study provides a baseline to promote environmental protection programs and pollution monitoring/control in Watershed and coastal areas.